Partial purification and characterization of cresolase and catecholase activity of black mulberrys (Morus nigra)

Polyphenol oxidase from Black mulberrys was extracted and partially purified through (NH4)2SO4 precipitation, dialysis and ion exchange chromatography. P-cresol was the better substrate for cresolase activity with a Km (11.5 mM) and catechol for catecholase activity with Km (6.4 mM) at pH 5. Km for cresolase and catecholase activity of IsoPPOII at pH 6.5 were 12 and 8.5 and for IsoPPOIII at pH 8 were 9.5 and 7.5 mM, respectively. Maximum of catalytic efficiency was obtained for cresolase activity of IsoPPOIII (92.4 unit.mg-1.mM-1) and minimum of catalytic efficiency was obtained for catecholase activity of IsoPPOII (42.9 unit.mg-1.mM-1). The enzyme showed high activity over a broad pH range of 3 – 9 so the optimum pH for PPO activity was found to be 5, 6.5 and 8. The optimal temperature for catecholase was found to be 45°C for IsoPPOIII but 40°C for IsoPPOII and IsoPPOI. Affinity of PPOs for various substrates varies widely. The enzyme showed a broad activity over a broad pH and temperature range. The thermal inactivation studies showed that the IsoPPOIII is heat resistant than IsoPPOII and IsoPPOI. The most potent inhibitors was kojic acid. Kojic acid is a potent inhibitor of IsoPPOIII ˃ IsoPPOII ˃ IsoPPOI.